Well if you have fins that are too big they will stiffen things up. If they are too small you end up losing drive, and possibly sliding around. Sometimes slide can be good if it can be controlled and is predictable, like you want hold through your bottom turn but some slide on a cut back can be fun.

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In a straight line your just going to get a little more drag off of bigger fins no matter your weight but once you start turning and pushing against the fin it's going to depend a lot on weight. In steep, powerful waves I don't think you need as much fin as you would in smaller, weaker waves where you need to generate speed. I'd probably use a smaller but more raked set in powerful, perfect waves as the wave in generating speed for you.

If you're too heavy for a small set of fins when you push hard against them they'll slip and release when you don't necessarily want them too and you'll be losing drive because they won't have the area to handle the forces you're putting against them. If you're using too big a fin it's going to feel stiff and slow through turns but could well fly straight down the line.

The drive, pivot and hold ratings on the FCS site are dependent on you using the correct size for your weight. If you used a large set when you should be on small you'd probably find lots of drive and hold but little pivot and they'd probably feel sticky on subtle movements and direction changes.

I'm no fin expert but that's what I think anyway. Bigger fronts with a small rear are a good remedy for that extra drive but still a looser tail.

Also it comes down to the template and the materials as much as the size of the fin. A smaller, very stiff fin with a more efficient template and foil is going to offer more drive and better release than a large, soft flexing fin with a big sweeping template. It's worth hunting for someone like Greg Griffin's comments on fin design. If you can sift through his vague answers and random remarks you can find some real gold.

my only 2 cents is that its important to remember that you only want to increase in size in a manner that reflects your weight and the size of your board and that there CAN be too much of a good thing. Meaning don't just jack up the area of your fin if you want speed, address it by paying attention to sweep, how the area is distributed across the template of the fin and also by paying attention the foiled vs flat fins...

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Has anyone here thrown five fins on their setup and taken it out into the surf? I'm wondering the pros and cons of that possible setup. I was kinda bored one day and added my deviant fin to my quad setup on the Hellfire 5'6". I was riding in Pamlico Sound with my buddies and found right off the bat that the setup seemed much faster than just the quad or thruster setup. Almost too fast for the choppy waters. Could this be specifically good for light winds in the waves?

Well I wasn't in the waves, I was just freestylin in the sound, but maybe it felt like more lift and less drag. I'm not trying to hypothesize, rather trying to get input from anyone else trying out 5 fins/